<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style>
        * {
            padding: 0;
            margin: 0;
            text-align: center;
        }

        .wrap {
            width: 500px;
            margin: 100px auto 0;
        }

        table {
            border-collapse: collapse;
            border-spacing: 0;
            border: 1px solid #c0c0c0;
            width: 500px;
        }

        th,
        td {
            border: 1px solid #d0d0d0;
            color: #404060;
            padding: 10px;
        }

        th {
            background-color: #09c;
            font: bold 16px "微软雅黑";
            color: #fff;
        }

        td {
            font: 14px "微软雅黑";
        }

        tbody tr {
            background-color: #f0f0f0;
            cursor: pointer;
        }
        
        .current {
            background-color: red!important;
        }
    </style>
</head>
<body>
    <div class="wrap">
        <table>
            <thead>
                <tr>
                    <th>序号</th>
                    <th>姓名</th>
                    <th>课程</th>
                    <th>成绩</th>
                </tr>
            </thead>
            <tbody id="target">
                <tr>
                    <td>
                        1
                    </td>
                    <td>吕不韦</td>
                    <td>语文</td>
                    <td>100</td>

                </tr>
                <tr>
                    <td>
                        2
                    </td>
                    <td>吕布</td>
                    <td>日语</td>
                    <td>100</td>
                </tr>
                <tr>
                    <td>
                        3
                    </td>
                    <td>吕蒙</td>
                    <td>营销学</td>
                    <td>100</td>
                </tr>
                <tr>
                    <td>
                        4
                    </td>
                    <td>吕尚</td>
                    <td>数学</td>
                    <td>100</td>
                </tr>
                <tr>
                    <td>
                        5
                    </td>
                    <td>吕雉</td>
                    <td>英语</td>
                    <td>100</td>
                </tr>
                <tr>
                    <td>
                        6
                    </td>
                    <td>吕超</td>
                    <td>体育</td>
                    <td>100</td>
                </tr>
            </tbody>
        </table>
    </div>

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        //需求：让tr各行变色，鼠标放入tr中，高亮显示。

        //1.隔行变色。
        var tbody = document.getElementById("target");
        var trArr = tbody.children;
        //循环判断并各行赋值属性（背景色）
        for(var i=0;i<trArr.length;i++){
            if(i%2!==0){
                trArr[i].style.backgroundColor = "#a3a3a3";
            }else{
                trArr[i].style.backgroundColor = "#ccc";
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            //鼠标进入高亮显示
            //难点：鼠标移开的时候要回复原始颜色。
            //计数器（进入tr之后，立刻记录颜色，然后移开的时候使用记录好的颜色）
            var color = "";
            trArr[i].onmouseover = function () {
                //赋值颜色之前，先记录颜色
                color = this.style.backgroundColor;
                this.style.backgroundColor = "#fff";
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            trArr[i].onmouseout = function () {
                this.style.backgroundColor = color;
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        }


    </script>


</body>
</html>